(CNN) -- As deliveries of the hotly anticipated iPhone 4 were set to begin, reports surfaced Monday of more problems with the Apple phone's ordering process.

Last week, AT&T, the exclusive wireless provider for the iPhone, suspended pre-orders after its system was overwhelmed.

On Monday, several technology websites reported receiving messages from readers that their iPhone pre-orders had been canceled without any further explanation.

Tech site Gizmodo printed an e-mail from AT&T that a reader reportedly forwarded to them. It read:

"Your iPhone order has been cancelled. Your credit card has not been charged. If you believe you have received this email in error, please return to the AT&T store where you placed your order. Sincerely, AT&T"

An AT&T spokesman said most of the cancellations were for people who accidentally submitted their order more than once or those who are eligible for an upgrade.

"We're reaching out to many of these customers to answer questions, and are also happy for customers to call us with individual account questions," spokesman Seth Bloom said in an e-mail to CNN.